1. Field of the Invention
The present invention relates generally to the field of printed circuit boards. More particularly, the present invention relates to multi-level printed circuit boards (or xe2x80x9cPCBsxe2x80x9d) that integrate optical data communications with other boards without electrical connections. That is, the present invention relates to backplane circuit boards that integrate photonic connection.
2. Background Information
Today, much of the world""s communication is carried on optical fibers, the data encoded in modulated light. Transmission rates are measured in billions of bits per second, until the data reaches its destination. There, the light is converted into electrical impulses so that it may be routed electronically. The result is lower data rates and increased delay.
Opto-electronic devices are being developed that incorporate waveguide structures on silicon substrates allowing for integration of light buses and electrical buses. These integrated devices will replace discrete components and make the transition from photon streams to electron streams more efficient and/or eliminate the transition altogether. Clearly, the ultimate efficiency will be achieved when no conversion from light to electrical signals is required, thus enabling communication as light from source to destination.
One of the impediments to achieving this objective is the backplane. The backplane is the interconnecting point for devices in a system and may be passive or intelligent. Typically, devices (sometimes referred to as xe2x80x9cdaughter boardsxe2x80x9d) are plug into a backplane through mechanical means. Additional cabling may be required to interconnect devices to each other or other points on the backplane resulting in slower data transfer rates, increased opportunities for failure, and increased costs. Opto-electronic devices require an electrical and/or an optical interface to the backplane.
Typically, backplanes and daughter boards are constructed on printed circuit boards (PCBs) on to which discrete components are mounted. What is needed are daughter-boards and backplanes constructed from PCBs that have both electrical and optical interfaces so as to eliminate additional cabling and to reduce or eliminate the need to convert from light signals to electrical signals. Such PCBs would also incorporate passive components such as multiplexers, demultiplexers, transducers and interferometers to effect optical signaling.
An object of the present invention is to integrate an optical transmitting material with a PCB to allow optical signals to be transmitted between circuit boards.
Another object of the present invention is to integrate optical polymers with PCB production to allow optical signal transmission.
Still another object of the present invention is to integrate a circuit board with an optical backplane to communicate using optical transmission to facilitate handling, insertion and removal of daughter boards without the need for connection cabling.
Yet another object of the present invention is to define optical transmitting polymers (optical waveguides) in a PCB by writing the connection scheme with a laser.
A further object of the present invention is to develop a method for producing PCBs integrated with optical waveguides using laser technology.
Yet a further object of the present invention is to develop a method for integrating optical waveguides with a PCB using successive laminations of optical conductive materials of differing refractive indices.
Still another object of the present invention is to use target marks on a copper layer to align optical waveguide positioning.
A PCB is designed to generate optical signals that allow an optical backplane to communicate with an inserted circuit board without use of electrical cabling. A surface or connector on the PCB is designed to allow transmission of light energy (signals). A preferred implementation is to use a polymer such as Polyguide(trademark). The polymer used needs to have good optical properties and high temperature resistance.
The PCB is laminated with a surface coat of a material having a specific refraction index, n2. In one embodiment of the present invention, the exterior laminate is a polymer material such as Polyguide(trademark). The polymer layer is laminated over a copper layer. The copper layer is roughed prior to lamination by chemical or mechanical or combination process to improve adhesion. The entire PCB surface is then covered with the polymer.
A second polymer layer is then layered on top of the first polymer layer. This layer has a different refraction index, n1 . The optical signal is transmitted in the second polymer layer.
The layers are then channeled by an automated method such as laser ablation. The channeling process leaves a void in the polymer layers. The copper layer is exposed where the dual polymer layers are channeled. Alignment of the laser ablation is to a recognizable pattern as a mark on the surface copper layer. The mark which is etched on the copper is a shape designed for easy recognition by the automated laser tools.
Those channels or voids are then filled in with the polymer having refraction index n2. The second polymer with the higher refraction index, n1, is sandwiched by the first polymer. The sandwiched polymer layer serves as an optical waveguide. The waveguide also incorporates other passive components such as multiplexers, de-multiplexers, transducers and interferometers to effect optical signaling.
Those locations where through-holes are to be drilled are channeled by a laser ablation process prior to the through hole drilling. The multi-layer PCB is finished by a final lamination of xe2x80x9cprepegxe2x80x9d and a copper foil deposit on both top and bottom. Then the through holes are drilled finishing the optical signal transmission.